The Brenner Base Tunnel (BBT) is a joint project built by Italy and Austria along the Munich-Verona axis. The planned 55 km long tunnel will be the world's second longest railway tunnel after the Gotthard Base Tunnel. Completion is scheduled for 2025.
The current Brenner railway has a small curve radius and a gradient of up to 31 per mill, limiting maximum train speed to 180 km/h. In order to relieve congestion on the Brenner highway by shifting freight traffic from the road to the railway, the BBT is designed as a shallow tunnel with a maximum gradient of six per mill. In the future, trains will be able to go through the tunnel at a maximum speed of up to 250 km/h. In addition, the capacity of freight transportation over the Brenner will be tripled.
Innsbruck-Ahrental exploratory tunnel
The BBT will have two 8.1 m wide single track tubes that are located at a distance of 70 m from each other. The Innsbruck-Ahrental exploratory tunnel has been constructed between the two tunnel tubes. It will supply important findings concerning the geological and hydrogeological conditions on site. During construction of the BBT tunnel tubes, the exploratory tunnel will also be used for removing excavated material. After completion of the BBT, the exploratory tunnel will be used for drainage.
The exploratory tunnel has a diameter of 5 to 6 m, a cross section of 26 m² and runs 12 m below the two planned main tubes. The tunnel is being excavated using blasting advance with four to five detonations per day. Approx. 45,000 m of self-drilling spiles in lengths of 3, 4 and 8 m have been used.
The construction project also included several access galleries that will divide the BBT into four sections and will provide access from outside for maintenance and emergency evacuation.